Semiconductor devices can be formed on silicon wafer substrates by the use of certain fabrication processes some of which involve the application of heat (e.g., in the range of 200.degree. C. to 1100.degree. C.) to the substrate in a controlled environment. Several processing methods for fabricating a device onto a substrate have evolved which include the application of thermal energy to the substrate to drive thermally activated fabrication processes. For instance, chemical-vapor deposition (CVD) processes can deposit various materials on a substrate, including metallic, semiconductor and insulating material layers. Thermal deposition processes and thermal anneal processes can support silicide formation. These chemical and thermal processes can form a microelectronic device such as an insulated gate field-effect transistor (IGFET) on a substrate by manipulating, forming or modifying materials such as silicon dioxide, silicon nitride, tungsten, polysilicon and other known materials. Well-known single-wafer rapid thermal processing (RTP) applications include rapid thermal annealing (RTA), rapid thermal oxidation (RTO), rapid thermal chemical-vapor deposition (RTCVD) processes, and rapid thermal nitridation (RTN).
During the formation of a device such as an IGFET on a substrate by thermal processing techniques such as RTP methods, consistent production of a high-quality semiconductor integrated circuit (IC) with high production yield is enabled when the thermal energy is applied in a uniform and repeatable manner. CVC, Inc. ("CVC") has introduced several significant improvements over conventional thermal processing systems and methods for semiconductor IC fabrication. For instance, CVC has developed a multi-zone radiant-energy illuminator for producing heat in silicon substrates during device fabrication as is disclosed in U.S. patent application Ser. No. 08/678,321 filed on Jul. 11, 1996, and entitled "Multi-Zone Illuminator for Rapid Thermal Processing," which is incorporated herein by reference as if fully set forth. This multi-zone illuminator provides improved wafer-to-wafer process and temperature repeatability as well as within-wafer temperature uniformity by monitoring and controlling optical energy produced by plural lamps arranged in multiple heating zones. The multi-zone illuminator also includes a multi-zone temperature measurement system having plural pyrometry sensors for real-time wafer temperature measurement.
Although the multi-zone illuminator provides improved device fabrication uniformity and repeatability, a number of process control difficulties remain with respect to fabrication by rapid thermal processing (RTP). For instance, in one implementation of rapid thermal processing ("RTP") or rapid thermal chemical-vapor deposition ("RTCVD"), a substrate is generally supported by a susceptor during the application of heat. The susceptor can absorb the radiant optical energy and redistribute thermal energy across the substrate thus nullifying or minimizing effectiveness of the control inputs to a multi-zone illuminator. Another limitation relates to the varying emissivity of the substrate during processing due to the dependence of substrate emissivity on temperature and thin films. Although CVC's multi-zone temperature sensing and control technology in conjunction with multi-zone illuminators can compensate for variations in wafer emissivity (due to any source such as temperature and/or material layers), this compensation can introduce some errors and requires complicated control algorithms which can depend upon extensive testing and calibration runs for each type of substrate being processed. Another difficulty relates to the size and makeup of the susceptor used to support a substrate. The heating susceptor can introduce residue contaminants (e.g., metallic contaminants) to the substrate when the susceptor is in physical contact with the substrate. Also, to provide adequate mechanical support of the substrate, the susceptor can be made of a relatively large mass of thermally conductive material. The larger the mass of a conventional heating susceptor, the more difficult it is to estimate and control the heat energy absorbed and emitted by the susceptor. Moreover, high-thermal-mass susceptors significantly slow down the wafer heating and cooling times, resulting in reduced wafer processing throughout.